There are two types of electric motors, synchronous motors and induction motors. Also, for the motor types, according to the difference in rotors, it is possible to classify them into a magnet type that uses a permanent magnet, a coil type for which a coil is wound, and a reactance type using a ferromagnetic body such as iron. The magnet type rotates by the permanent magnet of the rotor being drawn to the rotating magnetic field of the stator.
As a magnetic type synchronous motor, there is the compact synchronous motor noted in JP8-51745A, for example. This compact synchronous motor comprises a stator core for which a magnetization coil is wound, and a rotor including a magnet.
However, the conventional motors have increased weight compared to the generated torque, and when an attempt is made to increase the generated torque, there is the problem that the ratio of the generated torque and the weight significantly worsened. Furthermore, when using a higher magnetic flux density magnet, there is also the problem that due to the effect of core loss, this would not operate without the flow of a huge current at startup time.